1. Field
One or more aspects of embodiments according to the present invention relate to monopulse radar, and more particularly to a system and method for forming a monopulse radar delta beam using piecewise-linear weights.
2. Description of Related Art
Monopulse radar systems illuminate a target and receive the radar return with several different receiving antenna patterns, referred to as a sum beam, and one or more delta beams. A delta beam may have an antenna pattern with a null and phase reversal in the center of the pattern, so that the magnitude of the return in the delta beam provides a measure of the magnitude of the misalignment between the line of sight to the target and the center of the delta beam, and the phase of the delta beam return relative to the phase of the sum beam return provides an indication of the direction in which the line of sight to the target is misaligned with the center of the delta beam. Two delta beams may be used, one to measure misalignment in azimuth, for example, and one to measure misalignment in elevation.
A monopulse radar antenna may be an array antenna composed of a number of sub-arrays installed side by side, with a set of array element weights for each beam. The sum beam may be formed with a set of weights referred to as the sum weights, and a delta beam may be formed by applying an additional set of weights, referred to as the delta over sum (D/S) weights, so that each weight used in forming the delta beam is the product of a sum weight and a delta over sum weight. In related art systems, the delta over sum weights may differ from sub-array to sub-array, resulting in high manufacturing and maintenance costs associated with fabricating and maintaining a large number of distinct parts. In one related art approach, the sub-arrays are made identical and the delta over sum weights increase linearly across the array, with a single programmable weight per sub-array being the only difference between sub-arrays. This approach results in a reduction in manufacturing and maintenance costs, but these benefits are obtained at a cost in performance, e.g., in higher sidelobe levels (SLL).
Thus, there is a need for a monopulse radar system that provides good performance, and is constructed using identical sub-arrays.